Process and products for deliming limed pelts



Patented Dec. 16, 1941 UNITED STATES PATENT OFFICE PROCESS AND PRODUCTS FOR DELIMING LHVIED PELTS No Drawing.

Application February 1, 1939, Se-

rial No. 254,008. g In Germany February 7,

9 Claims.

The present invention relates to a process and products for delimingv limed pelts.

The elimination of the lime-from limed pelts is one of the most important operations which must be effected when the pelts are prepared for the tanning process. It is necessary that the pelts are delimed as quickly as possible and without damaging the hide material. The lime which remains in the pelts subjected to an incomplete deliming can bring about, as is known, various defectsappearlng in the course of further working up. With the carbonates or bicarbonates dissolved in the water, for instance, the lime easily forms insoluble precipitates which on the finished leather appear as lime blast, an inconvenience which is especially disagreeable in the case of fancy leather.

According to the known processes, deliming is effected by means of inorganic or organic acids, such as, for instance hydrochloric acid, sulfurous acid, sulfuric acid, formic acid, acetic acid, lactice acid, glycolic acid or butyric acid, which acids are used, if desired, in the form of their acid salts or their ammonium compounds, or also by means of the so-called bates, such as dungbates, pancreas extracts, bacterial bates or artificial bates. However, when these deliming agents are used, it cannot always be avoidedeven when most carefully working-that the hide substance is damaged to a' more or less high degree. Thus, the application of acids is,

as is known, often accompanied by a swelling of the pelts which may be undesirable in some cases, for instance inthe preparation of upper leather, whereas the application of bates leads I often, by the action of noxious bacteria, to the decomposition of proteins by which valuable hide material is lost. 1 e T Now, we have foundthat'water-soluble salts of amino-acids containing at least 2 organic radicals substituted by carboxyl' groups in alpha-- position to a basic nitrogen atom, are very suitable for deliming limed pelts. Acids of the above-indicated kind are, forinstance': nitrilotriacetic acid and its substitution products-such as C-methylor C-phenyl-nitrilo-triacetic acid, ethylene-bis-imino-diacetic acid, furthermore imino-diacetic acid and its derivatives substituted at the nitrogen. atom, for instance N-methy1-, N-butylimino-diacetic acid or 1-aminobenzene-N.N-diacetic acid-Z-carboxylic acid.

The salts of the above-named amino-carboxyli'c acids are distinguished by the'fact that they form water-soluble complex salts to bind the lime boundby the hide, the calcium compounds such as calcium carbonate present on the surface of the hide and the lime soap formed by decomposition of saponified hide fat. In this non-ionized form, the calcium is no longer capable of entering into reaction, so that reaction which might take place in the courseof the tanning process, for instance with the bicarbonates dissolved in the water or with tanning agents, are

excluded. Moreover, the high solubility of the complex compounds thus formed in water greatly facilitates their removal from the hide by treating it with water.

The hitherto known deliming agents are capable of removing only the lime which is mechanically bound to the hide or which is dis-' solved in the water absorbed by the capillary action of the hide.

The salts of the above-named, amino-carboxylic acids may also be used together withthe usual deliming agents or with the bating agents I is distinctly smoother.

such as cited above as examples. Small amounts of the amino-carboxylic acids are sufllcient for producing a very good effect. It has been ascertained that the deliming or bating process carried out in the usual way may considerably be improved and accelerated by addition of the above-defined amino-carboxylates. .This fact is 'of special advantage in case bating agents are used, since the simultaneous use of the new deliming agents considerably shortens the deliming process, the unfavorable influence of the bating agents ,upon the hide substance being, thereby, avoided to a great extent.

When the ,above-named products are added to the deliming bath, the pelts containing alkali or lime come down rapidly,'deliming is effected in a more uniform manner and, moreover, the feel of the material, especially that of the grain, In the present'process, the amino-carboxylates may be applied either before or after or also simultaneously with the usual deliming and bating agents. 4

' thereto:

The following examples serve to i lnstratethe invention,- but they are not intended to limit it Example 1 the ,trisodium s'altlof nitrilo-triacetic acid, calculated' upon the pelt weight; After a twelve hours treatment and after rinsing, the pelts are delimed and may directly be worked up.

Example 2 Limed cow pelts are, after soaking, delimed in a bath containing 2.5% of the tetrasodium salt of ethylene-bis-imino-diacetic acid, calculated upon the pelt weight. a

Eaiample 3 Limed calfskins are rinsed for a short time and then introduced into a bath containing 4% of the trisodium salt of 1-aminobenzene-N.N- diacetic acid-ortlro-carboxyllc acid, calculated upon the pelt weight. After a 20 hours treatment and subsequent rinsing, the material is delimed.

Example 4 Example 5 A 100 kg. of calfskins are limed in a lime-pit containing 1 cubic meter of water, 1 kg. of concentrated sodium sulfide and 6 kg. of quicklime; after rinsing, they are treated, for one hour with 0.300

kg. of glycolic acid of per cent. strength, 0.200

kg. of ammonium chloride, 0.050 kg. of the trisodium salt of nitrilo-triacetic acid and 200 liters of water having a temperature of 35 C. 0.300 kg. of a concentrated pancreas extract is then added to the same bath. .After one hour, the pelts are sufliciently delimed and bated; they are then rinsed in the usual manner and tanned. The grain of the pelts thus treated has a smoother feel than the pelts treated in the same manner, but without the addition of the trisodium salt of nitrilo-triacetic acid, the fat wrinkles being less evident.

Example 6 100 kg. of limed sheep pelts are treated with 200 liters of water having a temperature of 35 C., 1 kg. of lactic acid and 0.015 kg. of the trisodium salt of 1-aminobenzene-N.N-diacetic acidortho-carbox'ylic acid. After 1 hours, the pelts are well delimed and may, in this state, be subjected to tanning.

Example 7 100 kg. of cow pelts are fulled, for one hour, with 300-liters of water and 0.100 kg. of the tetra: sodium salt of ethylene-bis-imino-diacetic acid. The bath is then mixed with 0.100 kg. of hydrochloric acid and, after another hour, with 0.200 kg. of hydrochloric acid. After a further hour, the pelts are sufllciently free from lime for being subjected to further tanning. Pelts treated, for comparative purposes, without the addition of the tetra-sodium salt or ethylene-bis-imino-diacetic acid, show in the cut a considerably intenser red dyeing with phenolphthalein.

Example 8 100 kg. of cow pelts are lulled, ior'two hours,

with 1 kg. of ammonium chloride, 0.5 kg. of ammonium sulfate and 300 liters of water. After addition of 0.100 kg. of the trisodium salt of nitrilo-triacetic acid, the pelts are iulled for another three hours and then rinsed well.

Example 9 100 kg. of limed goat skins are fulled, for one hour, with 0.200 kg. oi! formic acid and'0.500 kg. of the tetrasodium salt of ethylene-bis-iminodiacetic acid and then rinsed for half-an-hour.

The pelts thus treated are distinguished by a smooth Iceland a good depletion.

Example 10 100 kg. of limed calfskins are rinsed and treated, for one hour, with 0200 kg. of a concentrated pancreas extract and 0.250 kg. of the trisodium salt of 'nitrilo-triacetic acid. After about hour's rinsing, the pelts maybe used for further tanning; they are distinguished by a I smooth feel of the grain .and byfa good depletion.

We claim: v

1. The process of deliming limed pelts which comprises treating the said pelts with solutions oi! water-soluble salts-oi carboxylic acids containing nitrogen and at least 2 organic radicals substituted by carboxyl a nitrogen atom.

2. The process of deliming limed pelts which comprises treating the said pelts with solutions of water-soluble salts of carboxylic acids containing nitrogen and at least 2 organic radicals substituted by carboxyl groups in alpha-position to a nitrogen atom, and subsequently rinsing the treated material. I

3. Deliming agents consisting essentially of water-soluble salts of carboxylic acids containing nitrogen and at least 2 organic radicals substituted by carboxyl groups in alpha-position to a nitrogen atom.

4. Deliming agents comprising a water-soluble salt of nitrilo-triacetic acid.

5. The process of deliming limed pelts which comprises treating said pelts with a solution of a water-soluble salt of nitrilo-triacetic acid.

6. The process of deliming limed pelts which comprises treating said pelts with a solution of a water-soluble salt of ethylene-bis-imino-diacetic acid.

'l. The process of deliming limed pelts which comprises treating said pelts with a solution of a water-soluble salt of l-aminobenzene-NN-diacetic acid-ortho-carboxylic acid. I

8. Deliming agents comprising a water-soluble salt of ethylene-bis-imino-diacetic acid. I

9. Deliming agents comprising a water-soluble salt of l-amino-benzene-NN-diacetic acid-orthocarboxylic acid.

. on'o mosxnu. WAL'I'ER PENSE.

groups in alpha-position to 

